The Athletics have lost a pair of rotation pieces in the past three days, placing lefties Sean Manaea (3.59 ERA, 160 2/3 innings) and Brett Anderson (4.02 ERA, 65 innings) on the disabled list due to a shoulder injury and a forearm strain, respectively. Since being placed on the DL on Sunday, Manaea has been determined to be suffering from tendinitis in his rotator cuff, manager Bob Melvin told reporters today (Twitter links via Jane Lee of MLB.com). He’s been shut down from throwing, and the A’s aren’t certain yet whether he’ll pitch again in 2018. Meanwhile, Anderson is set to undergo additional testing to evaluate his injury.

However, despite that pair of notable losses, the A’s aren’t likely to make a trade for a starter in advance of Friday’s deadline for postseason eligibility, tweets Ken Rosenthal of The Athletic. If there was any doubt based on that report, Oakland general manager David Forst went on record with Susan Slusser of the San Francisco Chronicle and, while he didn’t expressly rule out an addition, he characterized any such move as decidedly unlikely.

“We said when got Mike Fiers and Fernando Rodney how lucky we were that guys like that were available and we were able to make the deals,” said Forst. “And I don’t know if there is anything available outside the organization that can help us at this time.”

A look at the list of players known to have cleared revocable trade waivers reveals names such as Gio Gonzalez, Alex Cobb, Andrew Cashner, Francisco Liriano and Jordan Zimmermann as options to be freely traded. All five of those hurlers have under-performed to varying extents in 2018, and Cobb, Casnher and Zimmermann each come with undesirable contractual obligations beyond the current season. It’s possible, of course, that other arms have cleared or are currently on revocable trade waivers, but it doesn’t sound as though Forst and the A’s are keen on adding from outside the organization based on what’s currently available.

Internal options are the preferred route, it seems, but Forst made clear that top prospect Jesus Luzardo won’t be called upon to step into the starting mix. The 20-year-old Luzardo is among the game’s most highly regarded prospects, but he’s two and a half years removed from Tommy John surgery (March 2016) and has already seen an increase from 43 1/3 innings in 2017 to 109 1/3 innings in 2018. He’s made a rapid ascent to Triple-A, but his workload and importance to the Athletics’ long-term outlook are both understandable reasons for the Oakland brass to have some trepidation when weighing a potential promotion for Luzardo.

Forst indicated to Slusser that expanded September rosters could allow the A’s to utilize a bullpen-heavy approach to patching together the pitching staff. The Rays have already aggressively employed a bullpen-forward tactic in 2018, using relievers as “openers” and frequently leaning on bullpen days in lieu of a more traditional starting rotation. Such an arrangement is one of multiple approaches the A’s could contemplate when plotting out the remainder of the season. Relievers Yusmeiro Petit, Lou Trivino and Emilio Pagan are already accustomed to recording more than three outs per appearance.

[Related: Oakland Athletics depth chart]

For the time being, Oakland will plug right-handers Frankie Montas and Daniel Mengden into a starting staff that also includes Fiers, Trevor Cahill and Edwin Jackson. Chris Bassitt is the lone remaining healthy option on the 40-man roster, as the Athletics’ depth has been ravaged by injuries in 2018. Right-handers Kendall Graveman, Daniel Gossett and Jharel Cotton have all undergone Tommy John surgery, as has top left-handed pitching prospect A.J. Puk. Meanwhile, Andrew Triggs is on the 60-day DL due to a nerve injury, while Paul Blackburn has missed the past month-plus due to elbow issues.